The present invention relates generally to hydraulic control systems and, more specifically, to systems and methods for improving multifunction performance in hydraulic control systems.
Hydraulic control systems on mobile machines (e.g., earth moving machines or material handling machines) can use a pressure compensated load-sensing (PCLS) system with one fluid source (e.g., a hydraulic pump) and one control valve. Together the fluid source and the control valve control several cylinders and/or motors, typically known as functions, to move the machine in an intended motion.
The rate at which the hydraulic functions on the machines operate depend upon the cross-sectional area of control orifices of the hydraulic system and the pressure drop across those control orifices. To facilitate control, PCLS systems are typically designed with a load sense pressure signal and compensators to maintain an approximately constant pressure drop across those control orifices. In this way, flow from the fluid source is shared among the functions according to the ratio of each function's control orifice cross-sectional area to the sum of all the control orifice cross-sectional areas. Often the greatest of the workport pressures is selected as the load sense pressure. The fluid source will increase or decrease the output flow to maintain an approximately constant differential pressure between the fluid source output pressure and the load sense pressure. As the number of or size of the control orifices is changed, the fluid source flow must be changed to maintain this differential pressure.
When the maximum flow capacity of the fluid source is reached due to increases in the number of or cross-sectional areas of the control orifices, the supply of fluid to any given function will be reduced compared to the supply of fluid that function would receive if the fluid source were able to maintain the pressure differential. However, when the maximum fluid source capacity is reached, in some applications, it is desirable to maintain as great a flow as possible to certain functions, even at the expense of a greater flow reduction to the other functions.